FIGS. 42(a)-42(d) are diagrams illustrating a method for fabricating a semiconductor laser and for explaining a prior art method of etching a semiconductor. In these figures, reference numeral 101 designates a p type InP substrate. Numeral 102 designates a p type InP cladding layer. Numeral 103 designates an InGaAsP active layer. Numeral 104 designates an n type InP cladding layer. Numeral 105 designates an insulating film. Numeral 106 designates a first n type InP current blocking layer. Numeral 107 designates a p type InP current blocking layer. Numeral 108 designates a second n type InP current blocking layer. Numeral 109 designates a p type InP contact layer. Numeral 110 designates an n side electrode. Numeral 111 designates a p side electrode.
A description is given of the method for fabricating the prior art semiconductor laser. First of all, in the step of FIG. 42(a), on a p type InP substrate 101, a p type cladding layer 102, an active layer 103, and an n type cladding layer 104 are successively grown in an MOCVD (metal organic chemical vapor deposition) apparatus. Next, the wafer is taken out from the MOCVD apparatus, a stripe-shaped insulating film 105 is formed on the n type cladding layer 104, the wafer is etched in a liquid from the surface of the n type cladding layer 104 to the p type InP substrate 101, using the insulating film 105 as a mask, with a bromine methanol mixture or a sulfuric acid series etchant, thereby forming a mesa-stripe configuration as shown in FIG. 42(b). Further, in the step of FIG. 42(c), the wafer is returned to the MOCVD apparatus, and the n type InP current blocking layer 106, the p type InP current blocking layer 107, and the second n type InP current blocking layer 108 are selectively regrown to bury the mesa-stripe. Thereafter, the wafer is taken out of the MOCVD apparatus, the insulating film 105 is removed, the wafer is again returned to the MOCVD apparatus, and a contact layer 109 is formed on the mesa-stripe and the second n type InP current blocking layer 108. Further, an n side electrode 110 is formed on the surface of the contact layer 109 by evaporation and a p side electrode 111 is formed on the rear surface of the substrate 101, thereby forming a semiconductor laser as shown in FIG. 42(d).
Since, in this prior art method liquid phase etching using a bromine methanol mixture or a sulfuric acid series etchant is used, control of the etching rate is quite difficult and control of the remaining thickness is quite difficult. In addition, because the etching is carried out by using the etching solution, variations in etching depending on position on the wafer may arise, so the controllability of etching is difficult.
Carrying out the etching and regrowth of a compound semiconductor successively in the MOCVD apparatus in order to avoid oxidation of the regrowth interface and contamination has recently been studied. It was difficult to apply conventional liquid phase etching to etch a semiconductor layer in a semiconductor crystal growth apparatus such as an MOCVD apparatus in view of the structure of the apparatus.